This invention relates to electromechanical modules which include an integrated circuit (IC) package and a heat sink that is attached to the IC package in a removable fashion.
By an IC package is herein meant any type of enclosure of one or more IC chips which provides input/output (I/O) terminals for the enclosed chips. Some examples of IC packages which are commonly used in the electronics industry are dual in-line IC packages and pin grid array packages, both of which have I/O terminals that get soldered into via holes in a printed circuit board; and, plastic leaded chip carriers and leaded flat-packs, both of which have I/O terminals that get soldered onto the surface of a printed circuit board.
Often, in order to remove heat from the IC package, a heat sink is attached to the IC package in a permanent fashion such as with an epoxy or a solder. However, a problem with such a permanent attachment is that if the IC package and the heat sink are made of different materials, they will have different thermal expansion rates; and as a result, the attachment material and the IC package can be stressed and crack when they are subjected to temperature cycles.
To avoid the above thermal cracking problem, electromechanical modules have been developed in which a heat sink is attached to an IC package in a removable fashion which allows the heat sink and the IC package to slide against each other during temperature cycling. These modules are disclosed in U.S. Pat. No. 4,745,456 issued May 17, 1988 to Donald L. Clemens in his FIGS. 1 thru 14. However, although the Clemens' patent does teach how to solve the above described thermal cracking problem, all of the disclosed modules have several other drawbacks.
In particular, one of the drawbacks is that the footprint of the completed module is substantially larger than the footprint of the IC package by itself. By the term "footprint" is herein meant the area which the item in question occupies on a printed circuit board when that item is soldered to the printed circuit board. In the Clemens patent, the footprint of the completed module is substantially larger than the footprint of the IC package by itself because every embodiment includes a frame which is required to completely surround the IC package. This frame is shown in FIGS. 1, 9, and 14 respectively by reference numerals 32, 132, and 232. Consequently, when several of the Clemens' modules are soldered next to each other on a printed circuit board the frames of adjacent modules hit each other, and that reduces their density.
Another drawback of the Clemens, module is that the frame and the IC package must be assembled together before the IC package is soldered into a printed circuit board. This limitation occurs because in the Clemens' module, the I/O leads of the IC package must pass through the frame before the IC package is soldered to the printed circuit board, and, the frame gets trapped between the printed circuit board and the IC package. Likewise, after the Clemens' module is soldered to a printed circuit board, the frame cannot be removed without desoldering the IC package from the board.
Due to the above limitations, the removal of a defective module from a printed circuit board is made more difficult in comparison to the removal of just an integrated circuit package by itself. Likewise, the attachment to a printed board of an operable module is made more difficult than the attachment of just an operable integrated circuit package by itself. Why this is so is described in further detail in the detail description.
Accordingly, the primary object of the invention is to provide an electromechanical module with a small footprint and post-solder attachable/removable heat sink frame by which all of the above described problems are overcome.